Study of mangrove plants at Thung Kha Beach, Rayong province was made during November 2019 to February 2021. The objectives were to study species diversity and plants composition in mangrove forest. The four temporary sample plots, 20 X 50 m. were determined along the coastal.Twenty-three species belonging to 15 families and 20 genera were found. The most representative family in numbers of species found was Rhizophoraceae with 4 species. Plants density were 108.87 individual/Rai which diversity index in plot D had 1.93, plot A had 1.686, plot C had 1.684 and plot B had 1.428 respectively. Casuarina equisetifolia L. was a dominant species which the Important Value Index was 62.97. While, Terminalia catappa L. had the lowest diversity index was 2.53. A proportion of similarity index was 55.56 %. The results indicated that Thung Kha Beach mangrove had a quite perfect mangrove forest. In addition, Avicennia alba Blume, Sonneratia alba Sm. and Rhizophora were suitable planting for restoration forest and prevented coastal erosion.